Hepatitis C virus (HCV) infection is a major health problem in both developed and developing countries. It is estimated that about 1 to 5% of the world population is affected by the virus, amounting up to 175 million chronic infections worldwide. HCV infection appears to be the most important cause of transfusion-associated hepatitis and frequently progresses to chronic liver damage. Moreover, there is evidence implicating HCV in induction of hepatocellular carcinoma. Consequently, the demand for reliable diagnostic methods and effective therapeutic agents is high. There is also an urgent need to characterize new epitopes which can be used in the design of effective vaccines against hepatitis C.
HCV is a positive stranded RNA virus of about 9,8 kilobases which code for at least three structural and at least six non-structural proteins. The structural proteins have not yet been functionally assigned, but are thought to consist of a single core protein and two envelope proteins E1 and E2. The E1 protein consists of 192 amino acids and contains 5 to 6 N-glycosylation sites, depending on the HCV genotype, whereas the E2 protein consists of 363 to 370 amino acids and contains up to 11 N-glycosylation sites, depending on the HCV genotype (for review see Maertens and Stuyver, 1997).
The E1 and E2 proteins are currently not included in HCV antibody (Ab) assays, primarily because of their complex conformational structures which require expression in mammalian cells as well as non-denaturing purification techniques. Indeed, after expression of E2 in Escherichia coli, the reactivity of HCV sera with the recombinant protein ranged from 14 (Yokosuka et al., 1992) to 17% (Mita et al., 1992), whereas expression in eukaryotic systems yields reactivities of 13 to 97% (Inoue, 1992; Chien, 1993). Others demonstrated that the E1 protein expressed as a single protein from eukaryotic cells did not shown high reactivity with patient sera (from 6 to 60%; Kohara et al. (1992), Hsu et al. (1992), Chien et al. (1993)). We previously reported that high prevalences of Ab's to both of the purified recombinant E1 and E2 proteins, which were expressed in mammalian cells, could be found in sera from chronic hepatitis C patients (WO 96/04385 to Maertens et al.). In this regard, we also demonstrated that the majority of anti-E1 and anti-E2 antibodies in sera from HCV patients could not be mapped using 20-mer peptides (WO 96/04385 to Maertens et al.). Indeed, although all of the murine monoclonal Ab's against E1 could be mapped to reactivity with two 20-mer peptides, denoted as epitope A (amino acids (aa) 313-326) and epitope B (aa 208-224), at most 50% of patient sera reactive with recombinant proteins recognized epitope A and B. With regard to the E2 protein, only three out of twenty four murine monoclonal Ab's could be mapped using 20-mer peptides. These three Ab's were mapped to the hypervariable region I (HVR I) covered by peptide E2-67 (aa 394-413) and to a region covered by a peptide denoted E2-13B (aa 523-542). The remaining twenty-one Ab's could not be mapped using 20-mer peptides. The relative map positions of seven of these Ab's could be deduced from competition studies using recombinant E2 protein.
Taken together, it appears that anti-E1 and anti-E2 Ab's might be highly prevalent in sera of HCV patients. However, determining the presence of these Ab's is problematic due to the need to use eukaryotically expressed E1 and E2, which have to be purified using cumbersome non-denaturing techniques. As an alternative, chemically synthesized 20-mer peptides derived from the E1 and/or E2 proteins were produced. However, these synthesized 20-mer peptides were not able to recognize the anti-E1 and anti-2 Ab's in sera from HCV patients.
There is thus a need to design alternative methods to screen for HCV envelope Ab's.